This invention relates to optoelectronic coupling and signal regenerating devices for use in an optical communication system in which data is transmitted through optical data transmission lines; and more particularly, it relates to such optoelectronic coupling and signal-regenerating devices that are especially suited to be used in an optical communication system in which data are transmitted through bidirectional single optical fibers constituting the optical data transmission lines thereof.
Optical fibers are now becoming increasingly common in the field of data transmission, since they offer important advantages over the conventional electrical data transmission lines: they transmit radiant energy of high frequencies and hence are intrinsically capable of transmitting a larger amount of data per single line; further, they are virtually immune to adverse effects of electromagnetic noises.
In optical communication systems utilizing optical fibers as data transmission lines, repeaters may be installed along the transmission lines for the purpose of regenerating data signals and overcoming the attenuation thereof. Let us describe the organization of a typical bidirectional repeater in reference to FIG. 1, which shows diagramatically the organization of a conventional repeater for an optical communication system utilizing bidirectional single optical fibers; this repeater is disclosed, for example, in Japanese Laid Open Patent Application No. 60-49526.
In FIG. 1, the data is transmitted between the terminal stations A and B via the bidirectional single optical fibers 35 and 36 and a repeater 34 disposed therebetween. The repeater 34 comprises a switching unit 30, a monitoring and controlling unit 31, and a reproduction or regenerating unit 32 for amplifying and regenerating the optical signals When the transmission direction of signals is to be changed over, the switching unit 30 is operated by the monitoring and controlling unit 31 in response to a control signal outputted from one of the terminal stations A and 8. Namely, under the usual condition under which the data generated by the terminal station A is transmitted to the terminal station B, the switching unit 30 couples the ports of the optical fibers 35 and 36 to the input and the output of the regenerating unit 32 respectively, as shown in solid lines in the figure; thus, the signal supplied from the optical fiber 35 is amplified and regenerated by the regenerating unit 32 to be transmitted to the terminal station B via the optical fiber 36. When, on the other hand, the data is to be transmitted from the terminal station B to the terminal station A, the terminal station A outputs a change-over control signal; the monitoring and controlling unit 31, which is continuously monitoring the output of the regenerating unit 32, detects the change-over control signal and outputs a change-over command to the switching unit 30. In response thereto, the switching unit 30 is changed over to the coupling state shown by dotted lines in the figure, so that the port of optical fiber 36 is coupled to the input of the regenerating unit 32 and the output of the same unit 32 is coupled to the optical fiber 35. Thus, the signal outputted from the terminal station B is amplified and regenerated by the regenerating unit 32 to be transmitted to the terminal station A. In this manner, the repeater 34 is capable of regenerating signals that are transmitted in both the upward and downward directions, i.e., from terminal station B to terminal station A, and from terminal station A to terminal station B, respectively.
However, the conventional optical communication system utilizing bidirectional single optical fibers as data transmission lines has the following disadvantages. First, the control signal for changing over the switching unit 30 must be transmitted to the repeater 34 from other terminal stations; thus, the transmission of data between the stations requires complicated preliminary steps which reduces the efficiency of data transmission. Second, the repeater 34 must be provided with a monitoring and controlling unit 31; thus, the circuit organization of the repeater becomes complicated and the communication system is thereby made more expensive and large-sized.
The specific organization described above of the conventional repeater is applicable only to the case where the ports of the two data transmission lines are to be connected to each other via the repeater. Thus, the above-mentioned disadvantages are especially serious in the case where more than two ports of the data transmission lines are to be coupled to each other at the locations where the repeaters are to be provided.